Article - Sony VFETs part 1

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#722
juanitox said:
i' have just done it , sounds doesn't seems to suffer too much 😀
but i get better bass . i know it is different animals but the SITAMP 1 and 2 have 10K on the gate too 🙂
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Very interesting - have you measured the actual input impedance after the change? This would be nice to know as I plan to use a passive preamp without a buffer to the CSX1 and the static impedance of the Jensen being < 100R is a problem.
 
#724
Zen Mod said:
static impedance , meaning primary Rdc ........... is pretty much irrelevant

anyway , that value is giving some other info about performance , only to xperienced constructor
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Thanks ZM for weighing in.

Do you think I can use a passive preamp without implementing a buffer? My experience is that my passive needs about 25K to work properly. It's no problem to add the LSK buffer in Papa's paper, but just wondering.

Thanks.
 
#725
bottom of p.5 of article :

This figure is really excellent, but is dependent on the impedance of the source. Since you
are essentially driving the capacitance of the SITs themselves, you will find that a high
impedance source limits the bandwidth. A 600 ohm source impedance barely makes it to 20
Khz, so you will likely want a source impedance of 100 ohms or so to exceed 100 Khz.
Click to expand...

go figure

you need buffer
 
#730
thanks ZM you were right , i had one 2SK82 out of control with a lot of gain and distortion and the other low gain but clear sound .. i 'v just remember that i have made a short time 0V bias on the effective side ..
no free lunch this time 🙂
 
#732
Juanitox,

The SK180 are all very different and having no feedback the gain difference between two unmatched can be big.
I have here accummulated around twenty SK180 and I am afraid there will be only three more or less fitting pairs....
But I implemented simply a very small source resistor of 0R1 in the path of the SIT with the higher gain and I got them fairly equal......

🙂
 
#735
Listening update:

I have had a few friends over and they are amazed by the sound coming from the CSX1. It is so open and transparent and they can't get over how then can hear all the details in the sound. The amps have defiantly improved with some run time, becoming more open in the whole sound field. No talking heads in the middle, you are in the environment that the performance was recorded in. 🙂

As much as I love my F6, and it was better than the F5, I can say, I can't go back. I ordered another set of SITs and will make the F6 chassis into the common drain version when Nelson offers it to us. Bravo Nelson!
 
#736
Botte said:
Listening update:

I have had a few friends over and they are amazed by the sound coming from the CSX1. It is so open and transparent and they can't get over how then can hear all the details in the sound. The amps have defiantly improved with some run time, becoming more open in the whole sound field. No talking heads in the middle, you are in the environment that the performance was recorded in. 🙂

As much as I love my F6, and it was better than the F5, I can say, I can't go back. I ordered another set of SITs and will make the F6 chassis into the common drain version when Nelson offers it to us. Bravo Nelson!
Click to expand...

A little more context for my statement, I have 100dB speakers with a nice consistent 8 ohm impedance and don't need the damping offered by the F5 & F6. The SITs just make them sing!
 
#737
Botte said:
A little more context for my statement, I have 100dB speakers with a nice consistent 8 ohm impedance and don't need the damping offered by the F5 & F6. The SITs just make them sing!
Click to expand...

Very nice to hear that your CSX1 is making wonderful sounds. After my foray into some of the first modern implementations of 845 DHT amps 20 years ago, I learned that simplicity is always good! So a couple of questions: did you wind up using the LSK FE, and what sort of outcome would you estimate if the speaker were 4 Ohm and only 86dB sensitive?

I'm eagerly waiting for Part 2 (or Part n) as well so I don't have to change speakers....
 
#738
ci11 said:
So a couple of questions: did you wind up using the LSK FE, and what sort of outcome would you estimate if the speaker were 4 Ohm and only 86dB sensitive?
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I have not used the LSK folded cascode gain stage, just the regular CSX1 with the buffer on the input.

As for the lower sensitivity speakers, I think they would be fine if the impedance is even. You would most likely run out of power if you pushed them hard. I would think you would want something in the 90's at one watt for a better match. My two cents 🙂
 
#739
Botte said:
I have not used the LSK folded cascode gain stage, just the regular CSX1 with the buffer on the input.

As for the lower sensitivity speakers, I think they would be fine if the impedance is even. You would most likely run out of power if you pushed them hard. I would think you would want something in the 90's at one watt for a better match. My two cents 🙂
Click to expand...

That's why I am hoping the "Part 2" article will come out soon so my speakers will be happy, and I will be happy.

Thanks!
 
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